The invention relates generally to network congestion control.
As broadband access expands and the number of Web-enabled devices used by consumers grows, emerging powerline networking technology allows consumers to plug those devices into ordinary house electrical outlets, thus turning existing residential wiring into a high speed data network. Unlike more conventional networks like Ethernet networks, however, powerline networks are susceptible to unpredictable noise and interference from numerous sources, e.g., halogen lights, home appliances such a vacuum cleaners, and the like. Numerous appliances and computer equipment can be plugged in at any time, and those units can be turned on or off at any time, or operated for any amount of time. These types of changes throughout the day cause the powerline network transfer function to change almost constantly. When two powerline network nodes are involved in a communication, for example, a transmitting node is sending a frame over the powerline medium to a receiving node, a significant change in the powerline network transfer function occurring between the two nodes (e.g., when the receiving node suffers a loss of power or is unplugged) may mean that no response will be received from the receiving node for a frame that the transmitting network node attempts to transmit to that node over the powerline network under such conditions. If the powerline nodes implement the media access control protocol specified by the HomePlug 1.0 Specification, the transmitting node attempts several transmission “retries” using a more robust, reduced data rate transmission mode. During a “retry” period, the powerline bandwidth is reduced because of the transmission of the robust retry frames on the powerline. The reduced bandwidth causes congestion to occur at the transmitting node. Consequently, buffers may not be available in the transmitting node to store frames waiting to be transmitted to the receiving node and other nodes. Under these conditions, transmissions destined for other nodes, including nodes that are able to receive and respond to transmissions, are effectively blocked as well. In addition, if the transmitting node is a bridge that is still receiving frames from another network, it cannot empty its buffers until frame transmissions to the powerline network are completed. As a result, bridge congestion may cause back pressure to be exerted on that other network.